Our objective is to study the morphological basis of placental function, emphasizing the ways that cytoplasmic organization affects protein uptake, barrier integrity and steroid secretion. Specifically we will attempt to determine the mechanisms by which human syncytial trophoblast ingests proteins, emphasizing the role of surface coats and micropinocytotic vesicles. The intracellular localization of progesterone in the human placenta will be determined using immunochemical techniques. Comparative studies of placental cytology will be continued incuding a comparison of the diverse placental types in Chiroptera.